As is well known, carbon nanotubes are expected to be applied in various fields, including the field of electronics, as next-generation carbon materials having excellent characteristics in terms of electrical conductivity, thermal conductivity, mechanical strength, etc. However, carbon nanotubes easily and irreversibly aggregate (into bundles) due to the van der Waals force, for example, resulting in deteriorated characteristics and reduced workability, and this has been an obstacle to practical use. Methods for solving this problem have been intensively studied and developed. The point of solving the problem is how to deal with π-π interactions between carbon nanotubes induced by the π-surface of carbon nanotubes, which could be the factor that causes aggregation. Therefore, a method in which the surface of carbon nanotubes is chemically treated to modify the π-surface has been proposed. However, this method has a problem in that the chemical treatment on the surface of carbon nanotubes deteriorates the original characteristics of the carbon nanotubes. Further, as a different method, a method in which a surfactant having high affinity to the surface of carbon nanotubes, for example, is added as a dispersant to a solvent (an aqueous solvent, an organic solvent, etc.) together with carbon nanotubes, so that the dispersant molecules are located between carbon nanotubes in the solvent, thereby reducing or blocking π-π interactions between carbon nanotubes, has been proposed. This method is advantageous in that carbon nanotubes can be dispersed in a solvent without deteriorating their original characteristics. However, equilibrium is established in the association between carbon nanotubes and a dispersant, and their association is thus a dynamic, reversible phenomenon, while the association of carbon nanotubes (i.e., aggregation) is followed by precipitation and thus is a dynamic, irreversible phenomenon. Therefore, although the association of carbon nanotubes can be temporarily inhibited by the coexistence of carbon nanotubes with a dispersant in a solvent, the association of carbon nanotubes cannot be completely stopped. Accordingly, there is a problem in that carbon nanotubes reaggregate with time. Further, because carbon nanotubes are dispersed in a solvent, at the time of processing, there is a problem of how to handle the solvent. There also is a problem in that carbon nanotubes reaggregate during the handling of the solvent.
In recent years, as a novel method free from the problems that the above methods have, Patent Document 1 has proposed a method in which a shearing force is applied to carbon nanotubes for deagglomeration in the presence of an ionic liquid (a salt that is in a molten state at ambient temperature, which is also referred to as “ambient temperature molten salt” or simply as “molten salt”), thereby giving a gel containing carbon nanotubes. This method can be implemented in a simple manner such that carbon nanotubes and an ionic liquid are mixed and ground in a mortar. Also, carbon nanotubes are dispersed in a gel, and, because it is a gel, high workability is achieved. Accordingly, this method has been valued as an extremely useful method. However, as stated in Patent Document 1, to this method, the following three factors are indispensable: 1. in the presence of an ionic liquid, 2. carbon nanotubes are, 3. subjected to a shearing force and thus deagglomerated. According to Patent Document 1, when even one of these factors is not met, no gel is obtained. Thus, this method is inferior in terms of versatility. Specifically, as long as the use of an ionic liquid as a gelling medium is indispensable, the gelling medium must be selected from limited substances. In addition, because ionic liquids have electrical conductivity, although this method is suitable for application in a field where a gel with electrical conductivity is advantageous, the method is unsuitable for application in a field where a gel without electrical conductivity has more advantages. Further, no gel can be obtained in the cases of nano-carbon materials other than carbon nanotubes, such as carbon nanofibers and graphene. Further, the operation of applying a shearing force to carbon nanotubes for deagglomeration can be easily performed on a laboratory scale; however, on an industrial scale, even though Patent Document 1 states that a wet-milling apparatus or a kneader-type mixer can be used, such an operation is not always easy.